Electrical circuits using multi-gap cold cathode gas filled tubes



Oct. 22, 1957 JACKSON ETAL 2,810,861

ELECTRICAL CIRCUITS USING MULTI-GAP COLD CATHODE GAS FILLED TUBES FiledMarch 14, 1955 R5 g R2 Inventors M. JAC KSO N AD 00 u. By

Attorney 2,810,861 Patented Oct. 22, 1957 art (IRCUE'SS USsElG MULTI-GAPCOLD CATHQBDE GA FRIED TUBES Thomas P/i'eirion .laclrson and AlexanderDouglas Odell, London, England, assiguors to International StandardElectric corporaticn, New York, N. Y.

Application March 14, 1955, Serial No. 494,112

Claims priority, application Great Britain March 19, 1954 7 flairns.(Cl. 315S4.6)

The present invention relates to electrical circuits using multi-gapgas-filled discharge tubes of the type having an array ofinter-electrode gaps. In such tubes, suitablyapplied electrical pulsescause the discharge in the tube to be moved from gap to gap along thearray of gaps in a predetermined direction.

It has been found that when those tubes are used in circuits wherein thedischarge is allowed to remain at one gap for a relatively long period,there is a risk that the next pulse will not cause the correct movementof the discharge.

it is believed that this phenomenon is due to a leak discharge currentwhich flows in a gap ahead of the discharging gap, and it is an objectof the present invention to provide circuits wherein the adverse effectof this phenomenon is overcome.

According to the invention, therefore, We provide circuits for amulti-gap gas-filled discharge tube of the type referred to abovewherein the adverse effect of this is overcome by applying to the gapselectrical potentials which are such that during the intervals betweenthe pulses a substantial current is caused to flow in a gap ahead of thedischarging gap in the predetermined direction. This substantial currentis less than the normal discharge current.

The invention will now be described with reference to the singleaccompanying drawing, in which the commoned transfer cathodes of a tubehaving alternate transfer cathodes and storage cathodes are connected toa biasing potential of such a value that during the intervals betweenpulses a substantial current which is less than the normal dischargecurrent is caused to flow in a transfer gap ahead of the dischargingstorage gap in the intended direction of movement of the discharge.

The circuits described herein were developed for tubes such as aredescribed and claimed in United States Patent No. 2,553,585 (G. H.Hough). An example of such a tube is the GIG/241E tube, such as is soldunder the registered trademark Nomotron. These tubes have alternatestorage cathodes and transfer cathodes of which all transfer cathodesare internally commoned. The Gl/241E also has additional electrodesknown as control plates whose function is to control the area of thecathode glow, and to screen the discharge gaps from external influences.The invention is, of course, applicable to circuits using other tubes ofgenerally similar type, for instance, tubes without the control plates.

In the circuit shown, the transfer cathodes are biassed to a voltagenear to that of the discharging storage cathode. This has the resultthat when a storage cathode is discharging, a discharge exists betweenthe anode and the end of the transfer cathode immediately ahead of thatstorage cathode. This discharge is a substantial dis charge, i. e. ofthe order of hundreds of microamperes, but is less than the normaldischarge current.

In the normal driving circuits used hitherto, the transfer cathodes arebiassed to a value between the voltages of the positive and negativesupply terminals. Under these conditions a leak current flows from theend of a. transfer cathode ahead of the discharging storage cathode, andit is this leak current which causes the faulty operation referred toabove. The result of this 'operation is that in tubes of the type shownin the circuits when the Stepping pulse ends, the discharge may still beon the same storage cathode as it was before the pulse occurred. Thesubstantial current which has been mentioned as flowing in our modifiedcircuit which is less than the normal discharge current, overcomes thissticking of the discharge. Typical current values are 2.5-3.5milliamperes for the normal discharge currents, and 2G0500 microamperesfor this substantial current.

The tube MCT has its storage cathodes, four only of which are shown,each connected to earth via a resistorcapacitor circuit such as R1-C1,and its anode connected to a high positive voltage (e. g. 310 to 350volts) via two resistors in series R2. and R3. A capacitor C2 isconnected in parallel with R3. The commoned transfer cathodes areconnected to earth via a resistor R4 and via rectifiers MR1 and MR2 to apoint on a bleeder formed by resistors R5 and R6. The control plates (orcontrol plate where only one is provided) are connected to earth via aresistor R7.

The principle of the input circuit to the transfer cathodes is that thetransfer cathodes are biassed to a voltage near to the voltage of adischarging storage cathode. This has the result that when a storagecathode is discharging, a discharge exists between the anode and thetransfer cathode immediately ahead of that storage cathode. Thisdischarge, which is between the end of the aforementioned transfercathode adjacent the discharging storage cathode, is a substantialcurrent discharge which is of the order of 200500 microamperes, but isless than the normal discharge current.

At this point it is desirable to mention that although the conventionalsymbol adopted for the tube has an arrow-head for each transfer cathode,in the GIG/241E the storage cathodes are shaped to give directionaltransfer of the discharge, while the transfer cathodes are partiallyshaped to give directional transfer. Certain other forms of tube haveall cathodes shaped, while still others have none of the cathodes shapedand rely on external circuitry to ensure directional transfer.

Returning to the circuit shown the junction between rectifiers MR1 andMR2 is connected via a high value resistor to the positive supply. Theend of MR1 connected to the transfer cathodes is designated its anodeand the other end thereof its cathode. Hence the direction of how ofconventional current in which a rectifier such as Milli is in its lowresistance state is from anode to cathode. The bleeder resistors R5 andR6 are so proportioned that normally current flows through R8 and MR2.Normally MR1 is biassed to its high resistance condition by the currentflow just mentioned, so that the transfer cathodes are virtuallyisolated from the rest of the circuit. in this condition, the dischargementioned above from the end of the transfer cathode ahead of thedischarging storage cathode causes current flow through R4. The value ofR4 is such that the bias on the transfer cathodes is within a few voltsof the voltage of a discharging storage cathode.

The anode circuit of the tube t lCT includes, as men tioned above, acapacitor C2 which while the discharge is stationary on a storagecathode becomes charged to the voltage across R3. This arrangement hasbeen described and claimed in co-pending U. S. application No. 463,450filed October 2-3, 1954, T. M. Jackson-i. H. Fraser, now Patent No.2,749,479.

When a negative pulse (in one specific circuit of volts and having apulse width of 16 micro-seconds) is applied to the input terminal P, itreaches the junction of cause the correct movement of the discharge.

.vvill clearly vary' with theparticular gap arrangement.

3 MR1 and MR2 via capacitor C3. This pulse is eifectively applied to thetransfer cathodes of MCT via MR1,'which is in its low. resistance statefor a negative pulse. At the sflrne time MR2 is 'biassed to its: highresistance state.-

Since MR1 is in its high resistance state in'th e absence of V anegativepulse, these rectifiers serve to isolate the transfer cathodesuntil a'negative'pulse occurs. The negativepulse on the transfer cathodecauses, on its leading edge, the transfer cathodeahead of thedischargingstorage cathode (whichalre ady passes a-lowcurrent discharge) todischarge fully. The capacitor C2 discharges through the discharge pathof this transfer cathode, thereby providing an increased current flowduring the transfer'cathode dis- 7 charge; The discharge so producedfrom the transfer cathode'causes an increased voltage drop across theanodeload formed byresistors-R2 and R3. Since the capacitor in thecathode circuitofthe storage cathode cannot immediately discharge, thisreduces the potential across the previously-discharging storagecathode-anode gap to below thereto; a

flt will beremembered that the control plates are con- "nected tolearthvia a resistor R7. The portion of the control'plate near the dischargingcathode also passes current, when it is acting as a cathode, thedischarge being,

' of course, to the common anode. This discharge is a low currentdischarge of the order of hundreds of microamperesh It is employed, asis that of the transfer cathode,

to provide automatic bias for the electrode in question. Resistor R7 isso proportioned as to hold theipotential of the control plate to avoltage of the order of 70 volts. '--By' using this method of biassingthe control plate'sinstead of the hitherto-used bleeder, a considerableimprovement in operation has been obtained. 7

It should be'noted that MR1 and MR2 can'be replaced by other forms ofdiodes such as gas diodes or vacuum diodes.

It will be remembered that in the early part of the specification'it wasstated that when tubes of the type to which this invention is applicableare used in circuits wherein the discharge is allowed to remain at onegap for a relatively long period there is a risk thatthe next pulse willnot it was further stated in the opening paragraphs of the specificationthat this phenomenon is believed to be caused by a leak dischargecurrent flowing in a gap ahead of a dis charging gap. Such a low currentdischarge has the eifect of alteringthe discharge characteristics of-thegap in such a Way that the maintaining voltage of the gap is reduced,'Where the tube has transfer gaps interspersed with storage gaps theresult of this alteration of'the maintaining voltage is that when thepulse which should causetransfer away from the transfer gap ends, thedischarge may fail to transfer'from that gap in the desired direction.'This It has been noted that a discharge current of the same.

order of magnitude as the normal discharge current in a gap does notreduce the maintaining voltage of that gap. The reason why this is soalthough a much lower current does have this eifect is not understood.However, it has been found that if a current which is comparable in magnitude with, but of a noticeably lower value than, the

normal discharge current is allowed to flow in the gap immediately aheadof the discharging gap, then the troubles due to sticking are overcome.The reasons for'the success of this solution 'to the problem are, asalready men- IPA-circuit for a multi-cathode gas-filled electric dis- 7charge {tube of the type having a common anode and alternate storagecathodes and. transfer cathodes, which with'said anodes define an arrayof alternate storage gaps and transfer gaps, means for applying negativepotential pulses to said transfer cathodes in common for causing'thedi'sch'a'rge'to be moved from one storage gap to the next storage gapin'a'predetermined direction, means for ina suring the. stepping of thedischarge from a fired storage gap to a contiguous gap insaid'predetermined direction 7 cathodes from said pulse applicationmeans, and means i for. normally maintaining said isolating meansefiective' until application of a pulse from said source, whereby thetransfer gap contiguous to said fired gap is caused to fire. 2. A.circuit for a multi-cathode gas-filled electric discharge tube asclaimed in claim 1, wherein said isolating means comprises a firsttwo-pole unidirectional current carrying device having one pole coupledto said transfer cathodes andjpoledj to conduct current away frornsaidtransfer cathodes. i r

3.. A circuit for a multi-cathode gas-filled. electric discharge tube asclaimed in claim 2, wherein said means for normally maintaining .saidisolating means efiective comprises a'sour'ce of anode potential forsaid tube, voltage dividing means connected across said potentialsource, said dividing means comprising a second two-pole unidirectionalcurrent carrying device, the other pole of said firstunisdirectionaldevice connected to the oppositepole of saidsecondlunidirectionaldevice. a if 4. A circuit for a multi-cathodegas-filled electric discharge tubeasclaimed in claim 3, wherein saiduni-direc tional devices comprise metal rectifiers. V V i -5. A circuitfor a multi-cathode gas-filled electric discharge-tube as claimed inclaim 1, Whereinsaid biassing eans comprises aresistor connected betweensaid transfer cathodes and ground. 1 .6; A circuit for a multi-cathodegas-filled electric discharge tubeasclairned in claimli wherein saidmeans for insuring thestepping of thedischarge from a fired storage gapto a contiguous gap further comprises a source of anode potential forsaid tube, an anode load resistance coupled bctweenthepositive.terminal: of said potential' source'andsaid anode, and a capacitorconnected in par allel with jalportion of said load resistance remotefrom said anode, said capacitor. adapted to be normally charged toavoltageequal to thevoltage dropsacross said resistor portion, charge ins aid capacitoradapted.to increase he tta fersjansu upon fi iys su sap 57. A circuit for a multi-cathode gas-filled electric discharge tube asclaimed in claim 1, wherein said array further comprises controlelectrode means for limiting the discharge area of a fired cathode, andmeans for biassing said control electrode means.

References Cited in the file of this patent

